For example, a solid polymer electrolyte fuel cell employs an electrolyte membrane. The electrolyte membrane is a polymer ion exchange membrane, and is interposed between an anode and a cathode to form a membrane electrode assembly (MEA). The membrane electrode assembly is sandwiched between a pair of separators, so as to form a power generation unit. In use of the fuel cell of this type, normally, a predetermined number of power generation units are stacked together to form a fuel cell stack.
In the fuel cell, a fuel gas flow field is formed on a surface of one separator facing the anode for supplying a fuel gas to the anode, and an oxygen-containing gas flow field is formed on a surface of the other separator facing the cathode for supplying an oxygen-containing gas to the cathode. Further, a coolant flow field is formed between the adjacent separators for supplying a coolant along surfaces of the separators.
Further, in many cases, this type of fuel cell is constructed as the so-called “internal manifold type fuel cell”. In the internal manifold type fuel cell, a fuel gas supply passage and a fuel gas discharge passage for the fuel gas, an oxygen-containing gas supply passage and an oxygen-containing gas discharge passage for the oxygen-containing gas, and a coolant supply passage and a coolant discharge passage for the coolant extend through the power generation units in the stacking direction.
As an internal manifold type fuel cell, for example, a flow field plate as disclosed in Japanese Laid-Open Patent Publication No. 2008-536258 (PCT) is known. As shown in FIG. 19, a hydrogen flow field 2a is formed on the surface of an anode flow field plate 1a. At one end of the anode flow field plate 1a in a longitudinal direction indicated by an arrow X, an anode air inlet manifold aperture 3a, an anode coolant inlet manifold aperture 4a, and an anode hydrogen inlet manifold aperture 5a are formed. At the other end of the anode flow field plate 1a in the longitudinal direction, an anode air outlet manifold aperture 3b, an anode coolant outlet manifold aperture 4b, and an anode hydrogen outlet manifold aperture 5b are formed.
Further, in a fuel cell disclosed in Japanese Laid-Open Patent Publication No. 09-161819, as shown in FIG. 20, a separator 1b is provided in contact with the oxidizing agent electrode. A plurality of oxygen-containing gas flow grooves 2b are formed on a main surface of the separator 1b at the oxidizing agent electrode. Oxygen-containing gas inlets 6a are connected to the upstream side of the oxygen-containing gas flow grooves 2b, and oxygen-containing gas outlets 6b are connected to the downstream side of the oxygen-containing gas flow grooves 2b. 
One coolant water inlet 7a is formed between a pair of the oxygen-containing gas inlets 6a at an upper position of the separator b1, and one coolant water outlet 7b is formed between a pair of the oxygen-containing gas outlets 6b. A pair of fuel gas supply passages 8a are provided on both sides of an upper portion of the separator 1b, and a pair of fuel gas discharge passages 8b are provided on both sides of a lower portion of the separator 1b. 